There is a piece by Xenakis called Eonta which is for piano, 2 trumpets
and 3 trombones.  IMO this gets hands down my vote.  The opening statement
is marked 1/2 note = 60, and each 1/2 note is divided into sextuplets for
right hand and quintuplets for the left hand.  Every note has an individual
dynamic ranging from ppp to fff.  Many simultaneities have a different
dynamic for each note within the chord, and typically span a 12th or
greater, requiring a very fast arpeggiation.  Grace notes are frequent
(each with an individual dynamic of course).  This goes on unabated for 30
measures of 2/2 meter.  Should the pianist survive this, there is much more
of the same, with variations in the dynamics (some sections are uniformly
ppp, for example) and numbers of grace notes.  The composer notes that
parts of the piece including the opening solo were calculated on an IBM
7090 mainframe.  The miracle is that this work has actually been recorded,
I think by a Japanese pianist whose name I can't recall.  I have heard it,
but it's been a long time.  I cannot vouch for the accuracy, but I would
say to play it "perfectly" would be the most difficult technical task I
have seen in a PUBLISHED work including piano.  The score, for those
wishing to purchase it, is Boosey & Hawkes No.  799.

Chris Bonds